Dielectric layer forming method and devices formed therewith

ABSTRACT

Embodiments in accordance with the present invention provide alternative materials, and methods of forming such materials, that are effective as dielectric layers. Such embodiments include forming metal-containing dielectric layers over a silicon-containing substrate where a metal-containing layer is first formed and that treated to form a dielectric layer. Dielectric layers formed by methods of the present invention have a dielectric constant greater than that of silicon dioxide, and can have an equivalent oxide thickness of less than 2 nanometers. Such dielectric layers are useful in the forming of a variety of semiconductor devices such as transistors, capacitors and the like where such devices and integrated circuits formed from such devices are encompassed by embodiments in accordance with the present invention.

RELATED PATENT DATA

This patent resulted from a divisional application of U.S. patentapplication Ser. No. 09/881,408, filed on Jun. 13, 2001 now U.S. Pat.No. 7,037,862.

TECHNICAL FIELD

The present invention relates generally to methods of forming dielectriclayers and the devices fabricated therewith. More specifically, thepresent invention relates to methods of forming dielectric layers havinghigh dielectric constants by depositing oxidizable materials over asemiconductor substrate and oxidizing the materials to form amorphousoxides. The invention also pertains to devices formed employing suchoxides.

BACKGROUND

Increasing the performance of integrated circuits (ICs), both withregard to more complex functionality and higher speeds, is a primarygoal of efforts in advancing the semiconductor arts. One method that hasbeen extensively employed to achieve this goal is scaling, that isdecreasing area or size of individual device components that are used toform such integrated circuits. For example, the gate length of a typicalMOS transistor has been reduced over the past several years from severalmicrons to fractions of a micron and gate lengths of 0.1 micron or lesswill soon be desired. Such scaling efforts have also effected the sizeof capacitors used in a variety of ICs such as DRAMS and SRAMS (dynamicand static random access memories, respectively).

While such scaling efforts have resulted in the desired increases inperformance, generally such size reductions also impact at least somecharacteristics of the devices so “scaled.” For example, reducing thegate length of a transistor generally reduces the transistor's outputand decreasing the size of a capacitor generally reduces the capacitanceor amount of charge such a capacitor can store. Fortunately, changingother features of devices such as transistors and capacitors has made itpossible to retain or at least control such changes in theiraforementioned characteristics. Thus as transistor gate length has beenreduced, the gate dielectric layer's thickness has also been reduced toat least partially compensate for the change in device output.Similarly, as the size of capacitor structures has been reduced,materials such as hemispherically grained polysilicon (HSG) have beenemployed to increase the effective surface area of such structures andcompensate, at least in part, for such size reductions.

However, it appears likely that as scaling continues such exemplarycompensation techniques may not be possible. Silicon dioxide (SiO₂),with a dielectric constant of about 3.9, remains the most commonmaterial employed for gate dielectric layers. To maintain transistoroutput at an acceptable level, a transistor having a gate length of 0.1micron will require an ultra-thin SiO₂ layer with a thickness of about 2nanometers (nm). Ultra-thin being defined herein as a thickness of about5 nm or less.

The forming and use of such ultra-thin SiO₂ layers is problematic for avariety of reasons since such layers consist of only a few layers ofmolecules. Thus only one additional or missing layer of molecules canhave a dramatic effect on device performance; for example where adesired layer is four SiO₂ molecules thick, a change of one moleculewill change a characteristic such as the layer's capacitance by as muchas 25%. In addition, such thin layers typically exhibit high currentleakage, for example due to band to band or Fowler-Nordheim tunneling.Such layers are also more susceptible to dopant penetration or diffusionthrough the layer thus changing the characteristics of an adjacent layeror region; for example boron diffusion from the gate electrode into thechannel region alters channel characteristics.

One method of reducing these problems is the use of a thicker layer ofan alternative dielectric material such as a metal oxide having a higherdielectric constant than that of SiO₂. For the purpose of illustration,a metal oxide gate dielectric having an appropriately high dielectricconstant can be formed with a thickness several times that of a SiO₂layer while having the performance characteristics of the thinner SiO₂layer. Thus the thicker metal oxide layer is said to have the equivalentoxide thickness (EOT) of the thinner layer. Alternate metal oxidematerials such as titanium oxide (TiO₂), aluminum oxide (Al₂O₃),tantalum oxide (Ta₂O₅) and others have therefore received attention asreplacements for SiO₂. However, such alternate materials must exhibit,in addition to a high dielectric constant (greater than that of SiO₂), alarge band-gap with a favorable band alignment, low interface statedensity, good thermal stability and the ability to be formed in a mannerconsistent with known semiconductor process methods at reasonable costand yield. Unfortunately, many candidate metal oxide materials having anappropriately high dielectric constant, cannot meet these additionalrequirements. Thus it would desirable provide alternate dielectricmaterials and methods of forming such materials that are appropriate asa replacement for ultra-thin SiO₂ layers.

SUMMARY

Embodiments in accordance with the present invention provide dielectricmaterials, methods of forming such dielectric materials, andsemiconductor devices that employ such dielectric materials. Suchembodiments provide for the forming of a first metal-containingdielectric layer over a silicon-containing surface of a substrate andthe forming of a second metal-containing dielectric layer on the firstlayer. In embodiments of the present invention, the first and secondmetal-containing dielectric layers encompass elements selected fromGroup IVB and Group IIIB of the Periodic Table of Elements,respectively.

In some embodiments, a silicon dioxide layer is first formed and a firstmetal-containing layer is formed overlying such silicon dioxide layer.Advantageously, the metal of the first layer encompasses an element thatcan combine with the oxygen of the silicon dioxide to form a metal oxidematerial of the first metal-containing dielectric layer and chemicallyreduce the silicon dioxide to silicon.

In some embodiments in accordance with the present invention, one ormore metal-containing layers are exposed to an atmosphere thatencompasses oxygen while heating the exposed layers to a temperatureeffective to transform such metal-containing layers to metal-containingdielectric oxide layers. In some embodiments, such exposing encompassesion bombardment of the metal-containing layers, and in some embodimentssuch exposing encompasses providing oxygen radicals to themetal-containing layers.

Embodiments in accordance with the present invention provide for formingthe first and second metal-containing dielectric layers having a wideratio of relative thicknesses, for example from a ratio of about 1:5 toabout 5:1 or greater. In embodiments of the present invention, suchforming can be provided by physical vapor deposition (PVD) where ametal-containing layer of each formed layer is first deposited having athickness of about 10 nanometers (nm) or less. In embodiments of thepresent invention, such PVD methods include electron beam evaporationtechniques or other methods for forming high purity material layers byPVD. For example in some embodiments, radio frequency or microwaveenergy is employed for heating rather than an electron beam.

Embodiments of the present invention can encompass semiconductor devicessuch as MOS transistors, capacitors and the like. Such devices areformed using metal-containing dielectric layers in accordance with thepresent invention.

Some embodiments encompass integrated circuits such as dynamic andstatic random access memories (DRAMs and SRAMs) which includetransistors, capacitors and the like that are formed employingmetal-containing dielectric layers in accordance with the presentinvention, where such layers are also formed by methods in accordancewith the present invention. In some embodiments of the presentinvention, semiconductor devices encompassing a metal-containingdielectric layer have an equivalent oxide thickness (EOT) of 2 nm to 5nm. Advantageously, metal-containing dielectric layers in accordancewith the present invention having an EOT of less than 2 nm are alsopossible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments in accordance with the present invention are described belowwith reference to the following accompanying drawings.

FIG. 1 is a cross-sectional view of a semiconductor wafer fragmentdepicting an embodiment in accordance with the present invention at anearly step in the formation of a dielectric layer.

FIG. 2 is a cross-sectional view of a semiconductor wafer fragmentdepicting the embodiment of FIG. 1 at a subsequent step in the formationof a dielectric layer.

FIG. 3 is a cross-sectional view of a simplified representation of anMOS transistor formed in accordance with embodiments of the presentinvention.

FIG. 4 is a cross-sectional view of a simplified representation of acapacitor structure formed in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Embodiments in accordance with the present invention will be describedwith reference to the aforementioned figures. Various modifications,adaptations or variations of the specific methods and or structuresdescribed may become apparent to those skilled in the art as embodimentsof the present invention are described. All such modifications,adaptations or variations that rely upon the teachings of the presentinvention, and through which these teachings have advanced the art, areconsidered to be within the scope and spirit of the present invention.

To aid in interpretation of the description of the illustrations andclaims that follow, the term “semiconductor substrate” is defined tomean any construction encompassing silicon semiconductive material,including, but not limited to, bulk silicon semiconductive materialssuch as a silicon semiconductor wafer (either alone or in assembliesencompassing other materials thereon) and silicon semiconductivematerial layers (either alone or in assemblies encompassing othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductor substrates describedabove. In addition, the terms “high dielectric constant material” or“hi-K material” are used interchangeably herein and refer to materialshaving a dielectric constant that is greater than that of thermallygrown silicon dioxide, which is generally understood to have a value ofapproximately 3.9 or higher.

Referring to FIG. 1, semiconductor wafer fragment 10 a is shown depictedat an early processing step of an embodiment in accordance with thepresent invention. Wafer fragment 10 a encompasses a semiconductivesubstrate 20, shown having a surface 22, a silicon dioxide layer 30overlying surface 22, a first metal-containing layer 40 overlying layer30 and a second metal-containing layer 50 overlying layer 40.

As described above, semiconductive substrate 20 is defined to mean anyconstruction encompassing silicon semiconductive material. Generally across-sectional representation of such a semiconductive substrate 20,will include a variety of doped regions as are needed to formsemiconductor device structures. Some of such doped regions, for examplewell regions, being present even at an early stage of processing.However, for ease of understanding the present invention, such dopedregions that may be present are not shown in FIG. 1.

Surface 22 is an outermost boundary of substrate 20. For illustrativepurposes, surface 22 can be an upper surface of a single crystal siliconsubstrate, an epitaxially grown silicon layer or any other appropriatesilicon-containing material. Silicon dioxide layer 30 is an optionallayer. That is to say that, in some embodiments of the present inventionsuch a layer is present at this early stage in the processing and insome it is not present. In addition, it will be understood that in thoseembodiments where the optional silicon dioxide layer 30 is present, suchlayer is either a “native” oxide layer or an oxide layer that is formedto have a specific thickness by a process selected for the forming ofsuch a layer. Where silicon dioxide layer 30 is a “native” oxide layer,it will be understood that such a layer is formed spontaneously uponexposure of silicon surface 22 to an oxygen-containing ambient,generally at or near room temperature. Alternatively, where silicondioxide layer 30 is a purposely grown layer, such layer results fromexposure of surface 22 to oxidizing conditions such as an oxidizingambient, at an elevated temperature. Furthermore it will be understoodthat “native” oxide layers are essentially self-limiting in thicknessand are generally limited to about one or two molecular mono-layers inthickness. However, where layer 30 is a purposely grown layer, suchlayer can be formed having essentially any thickness and where employedin embodiments of the present invention, is typically grown to a fewnanometers in thickness, for example, 5 nanometers or less, although anyother thickness is also appropriate.

Generally, where electrical contact to surface 22 is desired, it isknown to remove such a layer as oxide layer 30 from over all or someportions of surface 22 prior to forming any layer from which theelectrical contact will be made. For example, Maiti et al. (U.S. Pat.No. 6,020,024, entitled “Method for Forming High Dielectric ConstantMetal Oxides,” hereinafter U.S. '024) state at column 2, lines 61–65,that semiconductor substrate 12 (FIG. 1) “has preferably beenpre-cleaned in order to minimize the oxide at its surface with an HFclean and/or hydrogen (H₂) anneal step. In an alternative, a plasma N₂Oprocess may be used to remove substrate native oxide.” As will bedescribed below, embodiments in accordance with the present inventioncan advantageously eliminate such a processing step. That is to say,that in some embodiments of the present invention, where a silicon oxidelayer 30 is formed or allowed to form, no specific removal step isneeded.

Still referring to FIG. 1, first metal-containing layer 40 is shownoverlying optional silicon oxide layer 30. Layer 40 is generally formedof a metal selected from the elements of Group IVB of the Periodic Tableof the Elements. As known, such group is generally understood to includethe elements titanium (Ti), zirconium (Zr), hafnium (Hf) andrutherfordium (Rf) which generally form chemically and thermally stableoxides having attractively high dielectric constants, for example theoxide of hafnium is reported to have a dielectric constant (k) of about27. While embodiments of the present invention encompass any of theGroup IVB elements, it has been found that a hafnium-containing layer 40is advantageous since (1) hafnium oxide (HfO₂) is the most stable oxideof the group of oxides, (2) hafnium is capable of reducing a siliconoxide layer, (3) hafnium silicide is readily oxidized and (4) HfO₂ isresistive to impurity. diffusion.

In some embodiments of the present invention, the thickness of layer 40will be 1 nanometer (nm) or less, while in other embodiments thethickness will be as much as approximately 5 nm or more. Such variationsin thickness are a function of, among other things, the use or non-useof the optional silicon dioxide layer 30, and the purpose for which afinally formed dielectric layer, in accordance with the presentinvention, is intended. For example, as will be discussed below, in someembodiments of the present invention a gate dielectric layer is formedand in other embodiments of the present invention a capacitor dielectriclayer is formed. As one of ordinary skill in the art is aware, thethickness of such layers can vary widely.

Metal-containing layer 40 is most advantageously formed by a physicalvapor deposition process (PVD). While any of the several common PVDprocesses such as sputtering or evaporation can be used, it is foundadvantageous to use an evaporative processes and in particular anelectron beam evaporative process. For example, where an electron beamevaporative process is employed, it is found that an initial puritylevel of the source material for the PVD process can be provided tolayer 40. That is to say that the level of purity of the source materialand initially deposited metal-containing layer is essentially unchanged.However, it will be understood that the other methods of formingmetal-containing layer 40 are within the scope and spirit of the presentinvention, for example evaporation methods where a heating source otherthan an electron beam is employed or any other appropriate PVD methodcapable of providing the initial purity level of the source material tolayer 40, can also be advantageously used.

Still referring to FIG. 1, second metal-containing layer 50 is shownoverlying first metal layer 40. In accordance with embodiments of thepresent invention, metal-containing layer 50 is advantageously formed ofa metal selected from the elements of Group IIIB of the Periodic Tableof the Elements. As known, Group IIIB is generally understood toencompass scandium (Sc), yttrium (Y), lanthanum (La) and actinium (Ac).Embodiments of the present invention encompass Group IIIB elements, assuch elements form dielectric oxides that have high thermodynamicstability and a generally suitable dielectric constant. Of such GroupIIIB elements, it has been found that a lanthanum-containing layer 50 isadvantageous at least because (1) lanthanum oxide (La₂O₃) has adielectric constant similar to that of HfO₂ (k=27 for La₂O₃ and k=24 forHfO₂) and (2) La₂O₃ has high thermodynamic stability. Thus changes inthe relative thickness for layers 40 and 50 that can change the ratio ofthicknesses for the layers from between about 1:5 to about 5:1, willresult in only small changes, if any, in the dielectric constant of thestacked oxide layer subsequently formed.

Generally, metal-containing layer 50 is formed in the same manner as ismetal-containing layer 40. That is to say, by using a physicaldeposition (PVD) method as previously described. However, while layers40 and 50 can be formed in distinct PVD processes, it is generallyadvantageous to form both layers using a single, unified PVD process.For example, such a unified deposition or forming process wouldgenerally provide that substrate 10 a is placed into a PVD system and amaterial of the first metal-containing layer 40 is formed thereon untila desired thickness of layer 40 is formed. In some embodiments, once afirst thickness of first layer 40 is obtained, the forming of firstlayer 40 is stopped and a forming of second layer 50 is begun within thesame PVD system. Subsequently, the forming of second layer 50 is stoppedonce a desired second thickness for such layer is obtained or when adesired total thickness of layers 40 and 50 is obtained.

In some embodiments, after the first thickness of layer 40 is formed,the forming of layer 50 is begun without a prior stopping of thedeposition of the material of layer 40. In this manner the material ofsecond metal-containing layer 50 will be combined with some material offirst metal-containing layer 40 in at least an interfacial region (notshown) of such second layer 50. It will be understood that in someembodiments, such a mixing of the materials of first layer 40 and secondlayer 50 is limited to such an interfacial region by stopping theforming of the material of layer 40 after the forming of the material oflayer 50 is started. In other embodiments, the forming of the materialof layer 40 is not stopped once the forming of the material of layer 50is started, rather both materials are formed until a desired thicknessis obtained thus, essentially all of second layer 50 is a mixture ofmaterials. In addition, as discussed for first metal-containing layer40, a desired thickness for second metal-containing layer 50 can alsovary as a function of the several factors mentioned for layer 40 as wellas the thickness of first layer 40 previously deposited. Thus, thethickness of such layer 50 generally has the same range as providedabove for the thickness of layer 40.

It has also been found that in some embodiments in accordance with thepresent invention a specific ratio of thickness for first layer 40 tosecond layer 50 is advantageous. For example where an optional siliconoxide layer 30 is used, generally a thin layer of a hafnium-containingmetal layer 40 is formed, about 1 nm or less, and employed to reducesuch silicon oxide layer 30 prior to forming second layer 50. Thesubsequent second metal-containing layer 50 is formed with anappropriate thickness, for example a layer of lanthanum-containing metalhaving a thickness of between about 3 to 5 nm. Advantageous thicknessratios of first metal-containing layer 40 to second metal-containinglayer 50 have been found to vary with ratios from about 1:5 to about 5:1being typical.

Turning now to FIG. 2, a cross-sectional view of a semiconductor waferfragment 10 b depicting the embodiment of FIG. 1 at a subsequentprocessing step is depicted. As shown, a first metal-containingdielectric layer 45 overlies surface 22 of semiconductive substrate 20and a second metal-containing dielectric layer 55 overlies the firstlayer 45.

First metal-containing dielectric layer 45 and second metal-containingdielectric layer 55 are formed from first metal-containing layer 40 andsecond metal-containing layer 50 (of FIG. 1), respectively. Generally, atransformation from metal-containing layers to metal-containingdielectric layers is performed. Such transformation typicallyencompassing oxidizing the metal-containing layers to form amorphousmetal oxide containing material layers. In some embodiments of thepresent invention, such an oxidation process is accomplished afterdeposition of both the first and second metal-containing layers. Inother embodiments oxidation of the first metal-containing layer to formthe first metal-containing dielectric layer precedes formation of thesecond metal-containing layer. In yet other embodiments of the presentinvention, oxidation of one or both of the metal-containing layers isperformed during the forming of one or the other of such layers. Bymeans of example, in one such method where optional silicon oxide layer30 is present, a hafnium-containing layer 40 is formed over layer 30 andsubsequently exposed to conditions such that the hafnium of layer 40combines with the oxygen of silicon oxide layer 30 to form ahafnium-containing dielectric layer 45 comprising hafnium oxide (HfO₂).Such a method of forming a metal oxide by the chemical reduction ofsilicon dioxide of layer 30 to silicon makes it possible to skip theseparate removal step for the silicon oxide layer that is taught byMaiti et al. in the previously mentioned U.S. '024. It will be notedthat since silicon dioxide layer 30 is reduced to silicon, the thicknessof such layer 30 is combined with substrate 20 in FIG. 2. When suchhafnium metal-containing layer is oxidized, a secondlanthanum-containing layer is formed and subsequently oxidized by anappropriate method. While such example specifically refers to Hf and La,it will be understood that the other elements of Group IVB and IIIB,such as Zr and Y, respectively, could also be employed, although therelative reactivity of the materials will vary.

Generally, conditions for the chemical reduction of optional siliconoxide layer 30 with the material of layer 40 encompass providingtemperatures between about 200° C. and 400° C. as an inert atmosphere istypically provided such that layer 30 is essentially the only source ofoxygen present. However, where silicon oxide layer 30 is not present, orafter the chemical reduction of such silicon dioxide layer, othermethods for the oxidation of portions of layer 40 not completelyoxidized and/or layer 50 are employed. Such other methods include, butare not limited to, the use of remotely formed oxygen radicals; ionbombardment of such metal layers with oxygen ions and thermal oxidationof such layers in an oxygen comprising atmosphere at appropriatetemperatures. Typically such low energy ion bombardment is performedusing relatively high plasma densities, typically above 10¹²/cm³, andlow electron temperature, generally less than 1.3 eV, and where oxygenradicals are used, generally such radicals are formed using appropriateradio frequency or microwave energy which is applied to an oxygencomprising gas stream at a reduced pressure. In addition, generally theuse of ion bombardment and/or oxygen radicals is provided in combinationwith a thermal treatment. By means of example, it is found effective toconvert metal-containing layers 40 and 50 to their respectivemetal-containing dielectric layers 45 and 55 by providing ionbombardment of the layers using a mixed gas with about 3% to 5% oxygenin an inert carrier such as Ar or Kr. The layers are held in such gasmixture at a pressure of about 1 Torr and a temperature of about 250° C.to about 300° C. with a microwave power source applying a power densityof about 3–7 W/cm². It will be understood that such oxidation conditionsonly one effective method and that other appropriate and effectivemethods can be used to form one or both of dielectric layers 45 and 55from layers 40 and 50 either collectively or individually.

Referring to FIG. 3, an MOS transistor 14 formed in accordance withembodiments of the present invention is depicted. Gate dielectric 60 isdisposed over a portion of surface 22 of substrate 20 as well asadjacent to and elevationally above source/drain (S/D) regions 24. Inaccordance with embodiments of the present invention, gate dielectric 60encompasses metal-containing dielectric layers 45 and 55 (FIG. 2) wheresuch layers are formed as described above and subsequently patternedusing any of the appropriate methods for patterning a gate electrode 80and dielectric 60. SID regions 24 and sidewall spacers 70 are alsoformed by appropriate methods. It will be understood that transistor 14is a simplified transistor representation, and that more complextransistor structures are also encompassed by embodiments of the presentinvention. For example, in some embodiments, transistor 14 is a MOSFEThaving an gate dielectric layer 60 that has an equivalent oxidethickness (EOT) of 2 nm or less while having an actual thickness of asmuch as about 6 nm. Such an advanced MOSFET can also have a gate lengthof about 0.25 micron or less and be encompassed within an integratedcircuit such as a dynamic random access memory (DRAM), static randomaccess memory (SRAM) or any of the various other memory integratedcircuits. Transistor 14 can also encompass a gate dielectric layer 60that has an EOT of greater than 2 nm and a gate length of more than 0.25micron.

Transistor or integrated circuit embodiments in accordance with thepresent invention that have an equivalent oxide thickness of about 2 nmor less, advantageously provide for readily forming gate dielectriclayer 60 having a desired EOT that would not be otherwise practical.Thus, methods for incorporating materials with high-dielectricconstants, such as oxides of Group IIIB and IVB metals, over a siliconsubstrate are provided where such materials can be formed into a stackedamorphous metal oxide-containing gate dielectric structure such as gatedielectric 60.

Turning now to FIG. 4 a simplified capacitor structure 16, formed inaccordance with embodiments of the present invention, is depicted.Capacitor structure 16 is shown overlying a doped region 26, disposed insemiconductive substrate 20. A lower capacitor electrode 82 electricallycontacts region 26, a capacitor dielectric 64 overlies electrode 82 anda second capacitor electrode 86 overlies capacitor dielectric 64.

Capacitor dielectric 64 is advantageously formed from first and secondmetal-containing layers deposited over lower electrode 82 in a manneranalogous to that described previously with FIGS. 1 and 2. Thus, afterfirst forming and patterning lower capacitor electrode 82, first andsecond metal-containing layers (not shown) are formed and transformed byappropriate methods into metal-containing dielectric layers which areencompassed within capacitor dielectric layer 64.

The previously described methods of converting Group IVB and IIIB metalsinto metal oxides are not limited to extremely thin films, thus thickermetal-containing layers, suitable for forming capacitor dielectriclayers having a thickness of 10 nm or more, can be first deposited andthen transformed into a metal-containing dielectric layer. As previouslymentioned, Group IVB metal oxides in general and HfO₂ in particular,are/is resistant to impurity diffusion so that such materials can beoxidized over a lower capacitor electrode 82 formed fromsilicon-comprising materials such as any of the various forms ofpolycrystalline silicon without oxidizing such lower electrode 82.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.In addition, advantages of the invention of the instant application havebecome apparent by and through the descriptions and examples provided.Thus it will be understood that the use of stacked amorphous gate oxidelayers formed of Group IVB and IIIB metal oxides advantageously providesa final layer that has a high dielectric constant of about 27 to 29, andis both thermally stable and protective of underlying layers to impuritydiffusion. It will be understood that the selection of Hf and La formthe metal-containing layers is particularly advantageous although othermetals from Group IVB and IIIB are also appropriate. It is to beunderstood, however, that the invention is not limited to the specificfeatures shown and described, since the means herein disclosed comprisepreferred forms of putting the invention into effect. The invention is,therefore, claimed in any of its forms or modifications within theproper scope of the appended claims appropriately interpreted inaccordance with the doctrine of equivalents.

1. A method for forming a MOS transistor, comprising: providing asemiconductor substrate having a surface comprising silicon; forming ahafnium-containing dielectric layer consisting of hafnium oxide on andin contact with the surface, such forming comprising initially forming ahafnium-containing metal layer; forming a lanthanum-containingdielectric layer on and in contact with the hafnium-containingdielectric layer, such forming comprising initially forming alanthanum-containing metal layer; and forming a gate electrode over thehafnium-containing and lanthanum-containing dielectric layers.
 2. Themethod of claim 1, where the forming the hafnium-containing metal layerand the forming the lanthanum-containing metal layer both comprisephysical vapor deposition.
 3. The method of claim 2, where physicalvapor deposition comprises electron beam evaporation.
 4. The method ofclaim 1, further comprising forming a layer of silicon dioxide over atleast a portion of the surface comprising silicon, prior to the formingof the hafnium-containing dielectric layer.
 5. The method of claim 1,where the forming the hafnium-containing dielectric layer and theforming the lanthanum-containing dielectric layer further compriseexposing the hafnium- and lanthanum-containing metal layers to an oxygencomprising atmosphere while heating the metal layers to a temperatureeffective to form a hafnium-containing dielectric layer and alanthanum-containing dielectric layer.
 6. The method of claim 5, whereforming the hafnium-containing dielectric layer and thelanthanum-containing dielectric layer comprise forming oxides of hafniumand lanthanum, respectively.
 7. The method of claim 6, where: thehafnium-containing metal layer is formed over a layer of silicondioxide; and further comprising providing conditions effective for thehafnium-containing metal layer to chemically reduce the layer of silicondioxide.
 8. The method of claim 6, further comprising: providing ionbombardment of the hafnium-containing metal layer and thelanthanum-containing metal layer using an ion bombardment energy ofabout 10 eV or less and where the heating to an effective temperaturecomprises heating while providing ion bombardment to a temperature fromabout 200° C. to about 400° C.
 9. The method of claim 6, where: theforming of the hafnium-containing metal layer comprises forming suchlayer having a thickness no greater than about 5 nanometers; the formingof the lanthanum-containing metal layer comprises forming such layerhaving a thickness no greater than about 5 nanometers; and a ratio and asum of the thicknesses of the hafnium-containing metal layer to thelanthanum-containing metal layer is from about 1 to 4 to about 4 to 1and no greater than about 6 nm, respectively.
 10. The method of claim 9where the thickness of the hafnium-containing metal layer is no greaterthan about 1 nm.
 11. The method of claim 9 where the hafnium-containingdielectric layer and the lanthanum-containing dielectric layer arecollectively a gate dielectric layer, where the gate dielectric layer isformed having an equivalent oxide thickness less than or equal to 2 nm.12. The method of claim 5, where the heating comprises heating thehafnium- and lanthanum-containing metal layers to a temperature fromabout 200° C. to about 400° C.
 13. A method for forming a MOStransistor, comprising: providing a semiconductor substrate having asurface comprising silicon; forming a dielectric layer consisting ofhafnium oxide overlying the surface; forming a dielectric layerconsisting of lanthanum oxide on and in contact with the hafnium oxidedielectric layer; and forming a gate electrode over the hafnium oxideand lanthanum oxide dielectric layers.
 14. A method for forming a MOStransistor, comprising: providing a semiconductor substrate having asurface comprising silicon; forming a layer consisting of hafnium on andin contact with the surface; oxidizing the hafnium layer into adielectric layer consisting of hafnium oxide; forming alanthanum-containing dielectric layer on and in contact with the hafniumoxide dielectric layer; and forming a gate electrode over the hafniumoxide and lanthanum-containing dielectric layers.
 15. A method forforming a MOS transistor, comprising: providing a semiconductorsubstrate having a surface comprising silicon; first forming ahafnium-containing layer and second forming a lanthanum-containing layerover the substrate, the first forming and the second formingencompassing physical vapor deposition; exposing the hafnium andlanthanum containing layers to an oxygen comprising atmosphere by ionbombardment of the hafnium-containing layer and the lanthanum-containinglayer using an energy of about 10 eV or less while heating the hafniumand lanthanum layers to a temperature from about 200 C. to about 400 C.to form oxides of hafnium and lanthanum as a hafnium-containingdielectric layer and a lanthanum-containing dielectric layer,respectively; and forming a gate electrode over the hafnium-containingand lanthanum-containing dielectric layers.